www.LinuxHowtos.org
FC
Section: POSIX Programmer's Manual (1P)Updated: 2013
Index Return to Main Contents
PROLOG
This manual page is part of the POSIX Programmer's Manual. The Linux implementation of this interface may differ (consult the corresponding Linux manual page for details of Linux behavior), or the interface may not be implemented on Linux.NAME
fc --- process the command history listSYNOPSIS
fc [-r] [-e editor] [first [last]] fc -l [-nr] [first [last]] fc -s [old=new] [first]
DESCRIPTION
The fc utility shall list, or shall edit and re-execute, commands previously entered to an interactive sh. The command history list shall reference commands by number. The first number in the list is selected arbitrarily. The relationship of a number to its command shall not change except when the user logs in and no other process is accessing the list, at which time the system may reset the numbering to start the oldest retained command at another number (usually 1). When the number reaches an implementation-defined upper limit, which shall be no smaller than the value in HISTSIZE or 32767 (whichever is greater), the shell may wrap the numbers, starting the next command with a lower number (usually 1). However, despite this optional wrapping of numbers, fc shall maintain the time-ordering sequence of the commands. For example, if four commands in sequence are given the numbers 32766, 32767, 1 (wrapped), and 2 as they are executed, command 32767 is considered the command previous to 1, even though its number is higher. When commands are edited (when the -l option is not specified), the resulting lines shall be entered at the end of the history list and then re-executed by sh. The fc command that caused the editing shall not be entered into the history list. If the editor returns a non-zero exit status, this shall suppress the entry into the history list and the command re-execution. Any command line variable assignments or redirection operators used with fc shall affect both the fc command itself as well as the command that results; for example:
-
fc -s -- -1 2>/dev/null
OPTIONS
The fc utility shall conform to the Base Definitions volume of POSIX.1-2008, Section 12.2, Utility Syntax Guidelines. The following options shall be supported:- -e editor
- Use the editor named by editor to edit the commands. The editor string is a utility name, subject to search via the PATH variable (see the Base Definitions volume of POSIX.1-2008, Chapter 8, Environment Variables). The value in the FCEDIT variable shall be used as a default when -e is not specified. If FCEDIT is null or unset, ed shall be used as the editor.
- -l
- (The letter ell.) List the commands rather than invoking an editor on them. The commands shall be written in the sequence indicated by the first and last operands, as affected by -r, with each command preceded by the command number.
- -n
- Suppress command numbers when listing with -l.
- -r
- Reverse the order of the commands listed (with -l) or edited (with neither -l nor -s).
- -s
- Re-execute the command without invoking an editor.
OPERANDS
The following operands shall be supported:- first, last
-
Select the commands to list or edit. The number of previous commands
that can be accessed shall be determined by the value of the
HISTSIZE
variable. The value of
first
or
last
or both shall be one of the following:
-
- [+]number
- A positive number representing a command number; command numbers can be displayed with the -l option.
- -number
- A negative decimal number representing the command that was executed number of commands previously. For example, -1 is the immediately previous command.
- string
- A string indicating the most recently entered command that begins with that string. If the old=new operand is not also specified with -s, the string form of the first operand cannot contain an embedded <equals-sign>. When the synopsis form with -s is used:
- *
- If first is omitted, the previous command shall be used. For the synopsis forms without -s:
- *
- If last is omitted, last shall default to the previous command when -l is specified; otherwise, it shall default to first.
- *
- If first and last are both omitted, the previous 16 commands shall be listed or the previous single command shall be edited (based on the -l option).
- *
-
If
first
and
last
are both present, all of the commands from
first
to
last
shall be edited (without
-l)
or listed (with
-l).
Editing multiple commands shall be accomplished by presenting to the
editor all of the commands at one time, each command starting on a new
line. If
first
represents a newer command than
last,
the commands shall be listed or edited in reverse sequence, equivalent
to using
-r.
For example, the following commands on the first line are equivalent to
the corresponding commands on the second:
-
-
fc -r 10 20 fc 30 40 fc 20 10 fc -r 40 30
-
-
- *
-
When a range of commands is used, it shall not be an error to specify
first
or
last
values that are not in the history list;
fc
shall substitute the value representing the oldest or newest command in
the list, as appropriate. For example, if there are only ten commands
in the history list, numbered 1 to 10:
-
-
fc -l fc 1 99
-
-
-
- old=new
- Replace the first occurrence of string old in the commands to be re-executed by the string new.
STDIN
Not used.INPUT FILES
None.ENVIRONMENT VARIABLES
The following environment variables shall affect the execution of fc:- FCEDIT
- This variable, when expanded by the shell, shall determine the default value for the -e editor option's editor option-argument. If FCEDIT is null or unset, ed shall be used as the editor.
- HISTFILE
- Determine a pathname naming a command history file. If the HISTFILE variable is not set, the shell may attempt to access or create a file .sh_history in the directory referred to by the HOME environment variable. If the shell cannot obtain both read and write access to, or create, the history file, it shall use an unspecified mechanism that allows the history to operate properly. (References to history ``file'' in this section shall be understood to mean this unspecified mechanism in such cases.) An implementation may choose to access this variable only when initializing the history file; this initialization shall occur when fc or sh first attempt to retrieve entries from, or add entries to, the file, as the result of commands issued by the user, the file named by the ENV variable, or implementation-defined system start-up files. In some historical shells, the history file is initialized just after the ENV file has been processed. Therefore, it is implementation-defined whether changes made to HISTFILE after the history file has been initialized are effective. Implementations may choose to disable the history list mechanism for users with appropriate privileges who do not set HISTFILE; the specific circumstances under which this occurs are implementation-defined. If more than one instance of the shell is using the same history file, it is unspecified how updates to the history file from those shells interact. As entries are deleted from the history file, they shall be deleted oldest first. It is unspecified when history file entries are physically removed from the history file.
- HISTSIZE
- Determine a decimal number representing the limit to the number of previous commands that are accessible. If this variable is unset, an unspecified default greater than or equal to 128 shall be used. The maximum number of commands in the history list is unspecified, but shall be at least 128. An implementation may choose to access this variable only when initializing the history file, as described under HISTFILE. Therefore, it is unspecified whether changes made to HISTSIZE after the history file has been initialized are effective.
- LANG
- Provide a default value for the internationalization variables that are unset or null. (See the Base Definitions volume of POSIX.1-2008, Section 8.2, Internationalization Variables for the precedence of internationalization variables used to determine the values of locale categories.)
- LC_ALL
- If set to a non-empty string value, override the values of all the other internationalization variables.
- LC_CTYPE
- Determine the locale for the interpretation of sequences of bytes of text data as characters (for example, single-byte as opposed to multi-byte characters in arguments and input files).
- LC_MESSAGES
-
Determine the locale that should be used to affect the format and contents of diagnostic messages written to standard error. - NLSPATH
- Determine the location of message catalogs for the processing of LC_MESSAGES.
ASYNCHRONOUS EVENTS
Default.STDOUT
When the -l option is used to list commands, the format of each command in the list shall be as follows:
-
"%d\t%s\n", <line number>, <command>
-
"\t%s\n", <command>
-
"\t%s\n", <continued-command>
STDERR
The standard error shall be used only for diagnostic messages.OUTPUT FILES
None.EXTENDED DESCRIPTION
None.EXIT STATUS
The following exit values shall be returned:- 0
- Successful completion of the listing.
- >0
- An error occurred. Otherwise, the exit status shall be that of the commands executed by fc.
CONSEQUENCES OF ERRORS
Default.The following sections are informative.
APPLICATION USAGE
Since editors sometimes use file descriptors as integral parts of their editing, redirecting their file descriptors as part of the fc command can produce unexpected results. For example, if vi is the FCEDIT editor, the command:
-
fc -s | more
-
HISTFILE=$HOME/.sh_hist$$
EXAMPLES
None.RATIONALE
This utility is based on the fc built-in of the KornShell. An early proposal specified the -e option as [-e editor [old= new ]], which is not historical practice. Historical practice in fc of either [-e editor] or [-e - [ old= new ]] is acceptable, but not both together. To clarify this, a new option -s was introduced replacing the [-e -]. This resolves the conflict and makes fc conform to the Utility Syntax Guidelines.- HISTFILE
- Some implementations of the KornShell check for the superuser and do not create a history file unless HISTFILE is set. This is done primarily to avoid creating unlinked files in the root file system when logging in during single-user mode. HISTFILE must be set for the superuser to have history.
- HISTSIZE
-
Needed to limit the size of history files. It is the intent of the
standard developers that when two shells share the same history file,
commands that are entered in one shell shall be accessible by the other
shell. Because of the difficulties of synchronization over a network,
the exact nature of the interaction is unspecified.
The initialization process for the history file can be dependent on the
system start-up files, in that they may contain commands that
effectively preempt the settings the user has for
HISTFILE
and
HISTSIZE.
For example, function definition commands are recorded in the history
file. If the system administrator includes function definitions in some
system start-up file called before the
ENV
file, the history file is initialized before the user can influence its
characteristics. In some historical shells, the history file is
initialized just after the
ENV
file has been processed. Because of these situations, the text requires
the initialization process to be implementation-defined.
Consideration was given to omitting the
fc
utility in favor of the command line editing feature in
sh.
For example, in
vi
editing mode, typing
dq<ESC>vdq
is equivalent to:
-
EDITOR=vi fc
-
32766: echo 1 32767: echo 2 1: echo 3
-
FUTURE DIRECTIONS
None.SEE ALSO
sh The Base Definitions volume of POSIX.1-2008, Chapter 8, Environment Variables, Section 12.2, Utility Syntax GuidelinesCOPYRIGHT
Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1, 2013 Edition, Standard for Information Technology -- Portable Operating System Interface (POSIX), The Open Group Base Specifications Issue 7, Copyright (C) 2013 by the Institute of Electrical and Electronics Engineers, Inc and The Open Group. (This is POSIX.1-2008 with the 2013 Technical Corrigendum 1 applied.) In the event of any discrepancy between this version and the original IEEE and The Open Group Standard, the original IEEE and The Open Group Standard is the referee document. The original Standard can be obtained online at http://www.unix.org/online.html .Any typographical or formatting errors that appear in this page are most likely to have been introduced during the conversion of the source files to man page format. To report such errors, see https://www.kernel.org/doc/man-pages/reporting_bugs.html .